1. Field of the Invention
This invention generally relates to an apparatus and method operative for electro-optically reading indicia having parts of different light reflectivity, for example, bar code or matrix array symbols, and, more particularly, to apparatus using both charge coupled device (CCD) technology and laser beam scanning technology for properly positioning, orienting and/or aiming such apparatus and reading one or two-dimensional bar code symbols, and to a method therefor.
2. Description of the Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. Such characters are typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control, and the like. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; 4,896,026, all of which have been assigned to the same assignee as the instant application.
As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand-held, portable laser scanning head supported by a user, which is configured to allow the user to aim the head, and more particularly, a light beam, at a target and a symbol to be read.
The light source in a laser scanner bar code reader is typically a gas laser or semiconductor laser. The use of semiconductor devices as the light source in scanning systems is especially desirable because of their small size, low cost and low voltage requirements. The laser beam is optically modified, typically by a focusing optical assembly, to form a beam spot of a certain size at the target distance. It is preferred that the cross section of the beam spot at the target distance be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol.
The bar code symbols are formed from bars or elements typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the bar code symbol is referred to as the density of the symbol. To encode a desired sequence of characters, a collection of element arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies, a unique "start" and "stop" character is used to indicate where the bar code begins and ends. A number of different bar code symbologies exist. These symbologies include UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5, etc.
For the purpose of our discussion, characters recognized and defined by a symbology shall be referred to as legitimate characters, while characters not recognized and defined by that symbology are referred to as illegitimate characters. Thus, an arrangement of elements not decodable by a given symbology corresponds to an illegitimate character(s) for that symbology.
In the laser beam scanning systems known in the art, the laser light beam is directed by a lens or similar optical components along a light path toward a target that includes a bar code or other symbol on the surface. The moving-beam scanner operates by repetitively scanning the light beam in a line or series of lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror, disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line or pattern across the symbol, or scan the field of view of the scanner, or do both.
Bar code reading systems also include a sensor or photodetector which functions to detect light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol and is detected and converted into an electrical signal. Electronic circuitry or software decode the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal detected by the photodetector may be converted into a pulse width modulated digital signal, with the widths corresponding to the physical widths of the bars and spaces. Such a digitized signal is then decoded based upon the specific symbology used by the symbol into a binary representation of the data encoded in the symbol, and subsequently to the alphanumeric characters so represented.
Moving-beam laser scanners are not the only type of optical instrument capable of reading bar code symbols. Another type of bar code reader particularly relevant to the present invention is one which incorporates detectors based upon charge coupled device (CCD) technology. In such prior art readers the size of the detector is typically smaller than the symbol to be read because of the image reduction by the objective lens in front of the CCD. The entire symbol is flooded with light from a light source such as light emitting diodes (LED) in the reader, and each CCD cell is sequentially read out to determine the presence of a bar or a space.
The working range of CCD bar code scanners can be rather limited as compared to laser based scanners and is especially low for CCD based scanners with an LED illumination source. Other features of CCD based bar code scanners are set forth in parent applications Ser. No. 07/317,553 filed Mar. 1, 1989, now abandoned and Ser. No. 07/717,771 filed Jun. 14, 1991, now U.S. Pat. No. 5,210,398; which are hereby incorporated by reference, and which are illustrative of the earlier technological techniques proposed for use in CCD scanners to acquire and read two-dimensional indicia.
It is a general object of the present invention to provide an improved indicia scanner without the limitations of prior art readers.
It is a further object of the present invention to provide an indicia scanner capable of providing the features of both a flying spot light beam scanner and an imaging scanner in a single unit.
It is yet another object of the invention to provide a hand-held indicia reader that is capable of aiming or being oriented and also imaging the field of view.
It is an even further object of the invention to provide a method which can be used to accomplish one or more of the above objectives.
Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detail description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications, modifications and embodiments in other fields, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.